/*
 *
 *  * Copyright (C) 2015 Square, Inc.
 *  *
 *  * Licensed under the Apache License, Version 2.0 (the "License");
 *  * you may not use this file except in compliance with the License.
 *  * You may obtain a copy of the License at
 *  *
 *  *      http://www.apache.org/licenses/LICENSE-2.0
 *  *
 *  * Unless required by applicable law or agreed to in writing, software
 *  * distributed under the License is distributed on an "AS IS" BASIS,
 *  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  * See the License for the specific language governing permissions and
 *  * limitations under the License.
 *
 */
package com.lark.oapi.okhttp;

import com.lark.oapi.okhttp.internal.Util;
import com.lark.oapi.okhttp.internal.publicsuffix.PublicSuffixDatabase;
import com.lark.oapi.okio.Buffer;

import javax.annotation.Nullable;
import java.net.*;
import java.nio.charset.Charset;
import java.util.*;

import static java.nio.charset.StandardCharsets.UTF_8;

/**
 * A uniform resource locator (URL) with a scheme of either {@code http} or {@code https}. Use this
 * class to compose and decompose Internet addresses. For example, this code will compose and print
 * a URL for Google search: <pre>   {@code
 *
 *   HttpUrl url = new HttpUrl.Builder()
 *       .scheme("https")
 *       .host("www.google.com")
 *       .addPathSegment("search")
 *       .addQueryParameter("q", "polar bears")
 *       .build();
 *   System.out.println(url);
 * }</pre>
 * <p>
 * which prints: <pre>   {@code
 *
 *     https://www.google.com/search?q=polar%20bears
 * }</pre>
 * <p>
 * As another example, this code prints the human-readable query parameters of a Twitter search:
 * <pre>   {@code
 *
 *   HttpUrl url = HttpUrl.parse("https://twitter.com/search?q=cute%20%23puppies&f=images");
 *   for (int i = 0, size = url.querySize(); i < size; i++) {
 *     System.out.println(url.queryParameterName(i) + ": " + url.queryParameterValue(i));
 *   }
 * }</pre>
 * <p>
 * which prints: <pre>   {@code
 *
 *   q: cute #puppies
 *   f: images
 * }</pre>
 * <p>
 * In addition to composing URLs from their component parts and decomposing URLs into their
 * component parts, this class implements relative URL resolution: what address you'd reach by
 * clicking a relative link on a specified page. For example: <pre>   {@code
 *
 *   HttpUrl base = HttpUrl.parse("https://www.youtube.com/user/WatchTheDaily/videos");
 *   HttpUrl link = base.resolve("../../watch?v=cbP2N1BQdYc");
 *   System.out.println(link);
 * }</pre>
 * <p>
 * which prints: <pre>   {@code
 *
 *   https://www.youtube.com/watch?v=cbP2N1BQdYc
 * }</pre>
 *
 * <h3>What's in a URL?</h3>
 * <p>
 * A URL has several components.
 *
 * <h4>Scheme</h4>
 *
 * <p>Sometimes referred to as <i>protocol</i>, A URL's scheme describes what mechanism should be
 * used to retrieve the resource. Although URLs have many schemes ({@code mailto}, {@code file},
 * {@code ftp}), this class only supports {@code http} and {@code https}. Use {@link URI
 * java.net.URI} for URLs with arbitrary schemes.
 *
 * <h4>Username and Password</h4>
 *
 * <p>Username and password are either present, or the empty string {@code ""} if absent. This
 * class offers no mechanism to differentiate empty from absent. Neither of these components are
 * popular in practice. Typically HTTP applications use other mechanisms for user identification and
 * authentication.
 *
 * <h4>Host</h4>
 *
 * <p>The host identifies the webserver that serves the URL's resource. It is either a hostname
 * like {@code square.com} or {@code localhost}, an IPv4 address like {@code 192.168.0.1}, or an
 * IPv6 address like {@code ::1}.
 *
 * <p>Usually a webserver is reachable with multiple identifiers: its IP addresses, registered
 * domain names, and even {@code localhost} when connecting from the server itself. Each of a
 * webserver's names is a distinct URL and they are not interchangeable. For example, even if {@code
 * http://square.github.io/dagger} and {@code http://google.github.io/dagger} are served by the same
 * IP address, the two URLs identify different resources.
 *
 * <h4>Port</h4>
 *
 * <p>The port used to connect to the webserver. By default this is 80 for HTTP and 443 for HTTPS.
 * This class never returns -1 for the port: if no port is explicitly specified in the URL then the
 * scheme's default is used.
 *
 * <h4>Path</h4>
 *
 * <p>The path identifies a specific resource on the host. Paths have a hierarchical structure like
 * "/square/okhttp/issues/1486" and decompose into a list of segments like ["square", "okhttp",
 * "issues", "1486"].
 *
 * <p>This class offers methods to compose and decompose paths by segment. It composes each path
 * from a list of segments by alternating between "/" and the encoded segment. For example the
 * segments ["a", "b"] build "/a/b" and the segments ["a", "b", ""] build "/a/b/".
 *
 * <p>If a path's last segment is the empty string then the path ends with "/". This class always
 * builds non-empty paths: if the path is omitted it defaults to "/". The default path's segment
 * list is a single empty string: [""].
 *
 * <h4>Query</h4>
 *
 * <p>The query is optional: it can be null, empty, or non-empty. For many HTTP URLs the query
 * string is subdivided into a collection of name-value parameters. This class offers methods to set
 * the query as the single string, or as individual name-value parameters. With name-value
 * parameters the values are optional and names may be repeated.
 *
 * <h4>Fragment</h4>
 *
 * <p>The fragment is optional: it can be null, empty, or non-empty. Unlike host, port, path, and
 * query the fragment is not sent to the webserver: it's private to the client.
 *
 * <h3>Encoding</h3>
 *
 * <p>Each component must be encoded before it is embedded in the complete URL. As we saw above,
 * the string {@code cute #puppies} is encoded as {@code cute%20%23puppies} when used as a query
 * parameter value.
 *
 * <h4>Percent encoding</h4>
 *
 * <p>Percent encoding replaces a character (like {@code \ud83c\udf69}) with its UTF-8 hex bytes
 * (like {@code %F0%9F%8D%A9}). This approach works for whitespace characters, control characters,
 * non-ASCII characters, and characters that already have another meaning in a particular context.
 *
 * <p>Percent encoding is used in every URL component except for the hostname. But the set of
 * characters that need to be encoded is different for each component. For example, the path
 * component must escape all of its {@code ?} characters, otherwise it could be interpreted as the
 * start of the URL's query. But within the query and fragment components, the {@code ?} character
 * doesn't delimit anything and doesn't need to be escaped. <pre>   {@code
 *
 *   HttpUrl url = HttpUrl.parse("http://who-let-the-dogs.out").newBuilder()
 *       .addPathSegment("_Who?_")
 *       .query("_Who?_")
 *       .fragment("_Who?_")
 *       .build();
 *   System.out.println(url);
 * }</pre>
 * <p>
 * This prints: <pre>   {@code
 *
 *   http://who-let-the-dogs.out/_Who%3F_?_Who?_#_Who?_
 * }</pre>
 * <p>
 * When parsing URLs that lack percent encoding where it is required, this class will percent encode
 * the offending characters.
 *
 * <h4>IDNA Mapping and Punycode encoding</h4>
 *
 * <p>Hostnames have different requirements and use a different encoding scheme. It consists of
 * IDNA mapping and Punycode encoding.
 *
 * <p>In order to avoid confusion and discourage phishing attacks, <a
 * href="http://www.unicode.org/reports/tr46/#ToASCII">IDNA Mapping</a> transforms names to avoid
 * confusing characters. This includes basic case folding: transforming shouting {@code SQUARE.COM}
 * into cool and casual {@code square.com}. It also handles more exotic characters. For example, the
 * Unicode trademark sign (™) could be confused for the letters "TM" in {@code http://ho™mail.com}.
 * To mitigate this, the single character (™) maps to the string (tm). There is similar policy for
 * all of the 1.1 million Unicode code points. Note that some code points such as "\ud83c\udf69" are
 * not mapped and cannot be used in a hostname.
 *
 * <p><a href="http://ietf.org/rfc/rfc3492.txt">Punycode</a> converts a Unicode string to an ASCII
 * string to make international domain names work everywhere. For example, "σ" encodes as "xn--4xa".
 * The encoded string is not human readable, but can be used with classes like {@link InetAddress}
 * to establish connections.
 *
 * <h3>Why another URL model?</h3>
 *
 * <p>Java includes both {@link URL java.net.URL} and {@link URI java.net.URI}. We offer a new URL
 * model to address problems that the others don't.
 *
 * <h4>Different URLs should be different</h4>
 *
 * <p>Although they have different content, {@code java.net.URL} considers the following two URLs
 * equal, and the {@link Object#equals equals()} method between them returns true:
 *
 * <ul>
 *   <li>http://square.github.io/
 *   <li>http://google.github.io/
 * </ul>
 * <p>
 * This is because those two hosts share the same IP address. This is an old, bad design decision
 * that makes {@code java.net.URL} unusable for many things. It shouldn't be used as a {@link
 * java.util.Map Map} key or in a {@link Set}. Doing so is both inefficient because equality may
 * require a DNS lookup, and incorrect because unequal URLs may be equal because of how they are
 * hosted.
 *
 * <h4>Equal URLs should be equal</h4>
 *
 * <p>These two URLs are semantically identical, but {@code java.net.URI} disagrees:
 *
 * <ul>
 *   <li>http://host:80/
 *   <li>http://host
 * </ul>
 * <p>
 * Both the unnecessary port specification ({@code :80}) and the absent trailing slash ({@code /})
 * cause URI to bucket the two URLs separately. This harms URI's usefulness in collections. Any
 * application that stores information-per-URL will need to either canonicalize manually, or suffer
 * unnecessary redundancy for such URLs.
 *
 * <p>Because they don't attempt canonical form, these classes are surprisingly difficult to use
 * securely. Suppose you're building a webservice that checks that incoming paths are prefixed
 * "/static/images/" before serving the corresponding assets from the filesystem. <pre>   {@code
 *
 *   String attack = "http://example.com/static/images/../../../../../etc/passwd";
 *   System.out.println(new URL(attack).getPath());
 *   System.out.println(new URI(attack).getPath());
 *   System.out.println(HttpUrl.parse(attack).encodedPath());
 * }</pre>
 * <p>
 * By canonicalizing the input paths, they are complicit in directory traversal attacks. Code that
 * checks only the path prefix may suffer!
 * <pre>   {@code
 *
 *    /static/images/../../../../../etc/passwd
 *    /static/images/../../../../../etc/passwd
 *    /etc/passwd
 * }</pre>
 *
 * <h4>If it works on the web, it should work in your application</h4>
 *
 * <p>The {@code java.net.URI} class is strict around what URLs it accepts. It rejects URLs like
 * "http://example.com/abc|def" because the '|' character is unsupported. This class is more
 * forgiving: it will automatically percent-encode the '|', yielding "http://example.com/abc%7Cdef".
 * This kind behavior is consistent with web browsers. {@code HttpUrl} prefers consistency with
 * major web browsers over consistency with obsolete specifications.
 *
 * <h4>Paths and Queries should decompose</h4>
 *
 * <p>Neither of the built-in URL models offer direct access to path segments or query parameters.
 * Manually using {@code StringBuilder} to assemble these components is cumbersome: do '+'
 * characters get silently replaced with spaces? If a query parameter contains a '&amp;', does that
 * get escaped? By offering methods to read and write individual query parameters directly,
 * application developers are saved from the hassles of encoding and decoding.
 *
 * <h4>Plus a modern API</h4>
 *
 * <p>The URL (JDK1.0) and URI (Java 1.4) classes predate builders and instead use telescoping
 * constructors. For example, there's no API to compose a URI with a custom port without also
 * providing a query and fragment.
 *
 * <p>Instances of {@link HttpUrl} are well-formed and always have a scheme, host, and path. With
 * {@code java.net.URL} it's possible to create an awkward URL like {@code http:/} with scheme and
 * path but no hostname. Building APIs that consume such malformed values is difficult!
 *
 * <p>This class has a modern API. It avoids punitive checked exceptions: {@link #get get()}
 * throws {@link IllegalArgumentException} on invalid input or {@link #parse parse()}
 * returns null if the input is an invalid URL. You can even be explicit about whether each
 * component has been encoded already.
 */
public final class HttpUrl {

    static final String USERNAME_ENCODE_SET = " \"':;<=>@[]^`{}|/\\?#";
    static final String PASSWORD_ENCODE_SET = " \"':;<=>@[]^`{}|/\\?#";
    static final String PATH_SEGMENT_ENCODE_SET = " \"<>^`{}|/\\?#";
    static final String PATH_SEGMENT_ENCODE_SET_URI = "[]";
    static final String QUERY_ENCODE_SET = " \"'<>#";
    static final String QUERY_COMPONENT_REENCODE_SET = " \"'<>#&=";
    static final String QUERY_COMPONENT_ENCODE_SET = " !\"#$&'(),/:;<=>?@[]\\^`{|}~";
    static final String QUERY_COMPONENT_ENCODE_SET_URI = "\\^`{|}";
    static final String FORM_ENCODE_SET = " \"':;<=>@[]^`{}|/\\?#&!$(),~";
    static final String FRAGMENT_ENCODE_SET = "";
    static final String FRAGMENT_ENCODE_SET_URI = " \"#<>\\^`{|}";
    private static final char[] HEX_DIGITS =
            {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'};
    /**
     * Either "http" or "https".
     */
    final String scheme;
    /**
     * Canonical hostname.
     */
    final String host;
    /**
     * Either 80, 443 or a user-specified port. In range [1..65535].
     */
    final int port;
    /**
     * Decoded username.
     */
    private final String username;
    /**
     * Decoded password.
     */
    private final String password;
    /**
     * A list of canonical path segments. This list always contains at least one element, which may be
     * the empty string. Each segment is formatted with a leading '/', so if path segments were ["a",
     * "b", ""], then the encoded path would be "/a/b/".
     */
    private final List<String> pathSegments;

    /**
     * Alternating, decoded query names and values, or null for no query. Names may be empty or
     * non-empty, but never null. Values are null if the name has no corresponding '=' separator, or
     * empty, or non-empty.
     */
    private final @Nullable
    List<String> queryNamesAndValues;

    /**
     * Decoded fragment.
     */
    private final @Nullable
    String fragment;

    /**
     * Canonical URL.
     */
    private final String url;

    HttpUrl(Builder builder) {
        this.scheme = builder.scheme;
        this.username = percentDecode(builder.encodedUsername, false);
        this.password = percentDecode(builder.encodedPassword, false);
        this.host = builder.host;
        this.port = builder.effectivePort();
        this.pathSegments = percentDecode(builder.encodedPathSegments, false);
        this.queryNamesAndValues = builder.encodedQueryNamesAndValues != null
                ? percentDecode(builder.encodedQueryNamesAndValues, true)
                : null;
        this.fragment = builder.encodedFragment != null
                ? percentDecode(builder.encodedFragment, false)
                : null;
        this.url = builder.toString();
    }

    /**
     * Returns 80 if {@code scheme.equals("http")}, 443 if {@code scheme.equals("https")} and -1
     * otherwise.
     */
    public static int defaultPort(String scheme) {
        if (scheme.equals("http")) {
            return 80;
        } else if (scheme.equals("https")) {
            return 443;
        } else {
            return -1;
        }
    }

    static void pathSegmentsToString(StringBuilder out, List<String> pathSegments) {
        for (int i = 0, size = pathSegments.size(); i < size; i++) {
            out.append('/');
            out.append(pathSegments.get(i));
        }
    }

    static void namesAndValuesToQueryString(StringBuilder out, List<String> namesAndValues) {
        for (int i = 0, size = namesAndValues.size(); i < size; i += 2) {
            String name = namesAndValues.get(i);
            String value = namesAndValues.get(i + 1);
            if (i > 0) {
                out.append('&');
            }
            out.append(name);
            if (value != null) {
                out.append('=');
                out.append(value);
            }
        }
    }

    /**
     * Cuts {@code encodedQuery} up into alternating parameter names and values. This divides a query
     * string like {@code subject=math&easy&problem=5-2=3} into the list {@code ["subject", "math",
     * "easy", null, "problem", "5-2=3"]}. Note that values may be null and may contain '='
     * characters.
     */
    static List<String> queryStringToNamesAndValues(String encodedQuery) {
        List<String> result = new ArrayList<>();
        for (int pos = 0; pos <= encodedQuery.length(); ) {
            int ampersandOffset = encodedQuery.indexOf('&', pos);
            if (ampersandOffset == -1) {
                ampersandOffset = encodedQuery.length();
            }

            int equalsOffset = encodedQuery.indexOf('=', pos);
            if (equalsOffset == -1 || equalsOffset > ampersandOffset) {
                result.add(encodedQuery.substring(pos, ampersandOffset));
                result.add(null); // No value for this name.
            } else {
                result.add(encodedQuery.substring(pos, equalsOffset));
                result.add(encodedQuery.substring(equalsOffset + 1, ampersandOffset));
            }
            pos = ampersandOffset + 1;
        }
        return result;
    }

    /**
     * Returns a new {@code HttpUrl} representing {@code url} if it is a well-formed HTTP or HTTPS
     * URL, or null if it isn't.
     */
    public static @Nullable
    HttpUrl parse(String url) {
        try {
            return get(url);
        } catch (IllegalArgumentException ignored) {
            return null;
        }
    }

    /**
     * Returns a new {@code HttpUrl} representing {@code url}.
     *
     * @throws IllegalArgumentException If {@code url} is not a well-formed HTTP or HTTPS URL.
     */
    public static HttpUrl get(String url) {
        return new Builder().parse(null, url).build();
    }

    /**
     * Returns an {@link HttpUrl} for {@code url} if its protocol is {@code http} or {@code https}, or
     * null if it has any other protocol.
     */
    public static @Nullable
    HttpUrl get(URL url) {
        return parse(url.toString());
    }

    public static @Nullable
    HttpUrl get(URI uri) {
        return parse(uri.toString());
    }

    static String percentDecode(String encoded, boolean plusIsSpace) {
        return percentDecode(encoded, 0, encoded.length(), plusIsSpace);
    }

    static String percentDecode(String encoded, int pos, int limit, boolean plusIsSpace) {
        for (int i = pos; i < limit; i++) {
            char c = encoded.charAt(i);
            if (c == '%' || (c == '+' && plusIsSpace)) {
                // Slow path: the character at i requires decoding!
                Buffer out = new Buffer();
                out.writeUtf8(encoded, pos, i);
                percentDecode(out, encoded, i, limit, plusIsSpace);
                return out.readUtf8();
            }
        }

        // Fast path: no characters in [pos..limit) required decoding.
        return encoded.substring(pos, limit);
    }

    static void percentDecode(Buffer out, String encoded, int pos, int limit, boolean plusIsSpace) {
        int codePoint;
        for (int i = pos; i < limit; i += Character.charCount(codePoint)) {
            codePoint = encoded.codePointAt(i);
            if (codePoint == '%' && i + 2 < limit) {
                int d1 = Util.decodeHexDigit(encoded.charAt(i + 1));
                int d2 = Util.decodeHexDigit(encoded.charAt(i + 2));
                if (d1 != -1 && d2 != -1) {
                    out.writeByte((d1 << 4) + d2);
                    i += 2;
                    continue;
                }
            } else if (codePoint == '+' && plusIsSpace) {
                out.writeByte(' ');
                continue;
            }
            out.writeUtf8CodePoint(codePoint);
        }
    }

    static boolean percentEncoded(String encoded, int pos, int limit) {
        return pos + 2 < limit
                && encoded.charAt(pos) == '%'
                && Util.decodeHexDigit(encoded.charAt(pos + 1)) != -1
                && Util.decodeHexDigit(encoded.charAt(pos + 2)) != -1;
    }

    /**
     * Returns a substring of {@code input} on the range {@code [pos..limit)} with the following
     * transformations:
     * <ul>
     *   <li>Tabs, newlines, form feeds and carriage returns are skipped.
     *   <li>In queries, ' ' is encoded to '+' and '+' is encoded to "%2B".
     *   <li>Characters in {@code encodeSet} are percent-encoded.
     *   <li>Control characters and non-ASCII characters are percent-encoded.
     *   <li>All other characters are copied without transformation.
     * </ul>
     *
     * @param alreadyEncoded true to leave '%' as-is; false to convert it to '%25'.
     * @param strict         true to encode '%' if it is not the prefix of a valid percent encoding.
     * @param plusIsSpace    true to encode '+' as "%2B" if it is not already encoded.
     * @param asciiOnly      true to encode all non-ASCII codepoints.
     * @param charset        which charset to use, null equals UTF-8.
     */
    static String canonicalize(String input, int pos, int limit, String encodeSet,
                               boolean alreadyEncoded, boolean strict, boolean plusIsSpace, boolean asciiOnly,
                               @Nullable Charset charset) {
        int codePoint;
        for (int i = pos; i < limit; i += Character.charCount(codePoint)) {
            codePoint = input.codePointAt(i);
            if (codePoint < 0x20
                    || codePoint == 0x7f
                    || codePoint >= 0x80 && asciiOnly
                    || encodeSet.indexOf(codePoint) != -1
                    || codePoint == '%' && (!alreadyEncoded || strict && !percentEncoded(input, i, limit))
                    || codePoint == '+' && plusIsSpace) {
                // Slow path: the character at i requires encoding!
                Buffer out = new Buffer();
                out.writeUtf8(input, pos, i);
                canonicalize(out, input, i, limit, encodeSet, alreadyEncoded, strict, plusIsSpace,
                        asciiOnly, charset);
                return out.readUtf8();
            }
        }

        // Fast path: no characters in [pos..limit) required encoding.
        return input.substring(pos, limit);
    }

    static void canonicalize(Buffer out, String input, int pos, int limit, String encodeSet,
                             boolean alreadyEncoded, boolean strict, boolean plusIsSpace, boolean asciiOnly,
                             @Nullable Charset charset) {
        Buffer encodedCharBuffer = null; // Lazily allocated.
        int codePoint;
        for (int i = pos; i < limit; i += Character.charCount(codePoint)) {
            codePoint = input.codePointAt(i);
            if (alreadyEncoded
                    && (codePoint == '\t' || codePoint == '\n' || codePoint == '\f' || codePoint == '\r')) {
                // Skip this character.
            } else if (codePoint == '+' && plusIsSpace) {
                // Encode '+' as '%2B' since we permit ' ' to be encoded as either '+' or '%20'.
                out.writeUtf8(alreadyEncoded ? "+" : "%2B");
            } else if (codePoint < 0x20
                    || codePoint == 0x7f
                    || codePoint >= 0x80 && asciiOnly
                    || encodeSet.indexOf(codePoint) != -1
                    || codePoint == '%' && (!alreadyEncoded || strict && !percentEncoded(input, i, limit))) {
                // Percent encode this character.
                if (encodedCharBuffer == null) {
                    encodedCharBuffer = new Buffer();
                }

                if (charset == null || charset.equals(UTF_8)) {
                    encodedCharBuffer.writeUtf8CodePoint(codePoint);
                } else {
                    encodedCharBuffer.writeString(input, i, i + Character.charCount(codePoint), charset);
                }

                while (!encodedCharBuffer.exhausted()) {
                    int b = encodedCharBuffer.readByte() & 0xff;
                    out.writeByte('%');
                    out.writeByte(HEX_DIGITS[(b >> 4) & 0xf]);
                    out.writeByte(HEX_DIGITS[b & 0xf]);
                }
            } else {
                // This character doesn't need encoding. Just copy it over.
                out.writeUtf8CodePoint(codePoint);
            }
        }
    }

    static String canonicalize(String input, String encodeSet, boolean alreadyEncoded, boolean strict,
                               boolean plusIsSpace, boolean asciiOnly, @Nullable Charset charset) {
        return canonicalize(input, 0, input.length(), encodeSet, alreadyEncoded, strict, plusIsSpace,
                asciiOnly, charset);
    }

    static String canonicalize(String input, String encodeSet, boolean alreadyEncoded, boolean strict,
                               boolean plusIsSpace, boolean asciiOnly) {
        return canonicalize(
                input, 0, input.length(), encodeSet, alreadyEncoded, strict, plusIsSpace, asciiOnly, null);
    }

    /**
     * Returns this URL as a {@link URL java.net.URL}.
     */
    public URL url() {
        try {
            return new URL(url);
        } catch (MalformedURLException e) {
            throw new RuntimeException(e); // Unexpected!
        }
    }

    /**
     * Returns this URL as a {@link URI java.net.URI}. Because {@code URI} is more strict than this
     * class, the returned URI may be semantically different from this URL:
     *
     * <ul>
     *     <li>Characters forbidden by URI like {@code [} and {@code |} will be escaped.
     *     <li>Invalid percent-encoded sequences like {@code %xx} will be encoded like {@code %25xx}.
     *     <li>Whitespace and control characters in the fragment will be stripped.
     * </ul>
     *
     * <p>These differences may have a significant consequence when the URI is interpreted by a
     * webserver. For this reason the {@linkplain URI URI class} and this method should be avoided.
     */
    public URI uri() {
        String uri = newBuilder().reencodeForUri().toString();
        try {
            return new URI(uri);
        } catch (URISyntaxException e) {
            // Unlikely edge case: the URI has a forbidden character in the fragment. Strip it & retry.
            try {
                String stripped = uri.replaceAll("[\\u0000-\\u001F\\u007F-\\u009F\\p{javaWhitespace}]", "");
                return URI.create(stripped);
            } catch (Exception e1) {
                throw new RuntimeException(e); // Unexpected!
            }
        }
    }

    /**
     * Returns either "http" or "https".
     */
    public String scheme() {
        return scheme;
    }

    public boolean isHttps() {
        return scheme.equals("https");
    }

    /**
     * Returns the username, or an empty string if none is set.
     *
     * <p><table summary="">
     * <tr><th>URL</th><th>{@code encodedUsername()}</th></tr>
     * <tr><td>{@code http://host/}</td><td>{@code ""}</td></tr>
     * <tr><td>{@code http://username@host/}</td><td>{@code "username"}</td></tr>
     * <tr><td>{@code http://username:password@host/}</td><td>{@code "username"}</td></tr>
     * <tr><td>{@code http://a%20b:c%20d@host/}</td><td>{@code "a%20b"}</td></tr>
     * </table>
     */
    public String encodedUsername() {
        if (username.isEmpty()) {
            return "";
        }
        int usernameStart = scheme.length() + 3; // "://".length() == 3.
        int usernameEnd = Util.delimiterOffset(url, usernameStart, url.length(), ":@");
        return url.substring(usernameStart, usernameEnd);
    }

    /**
     * Returns the decoded username, or an empty string if none is present.
     *
     * <p><table summary="">
     * <tr><th>URL</th><th>{@code username()}</th></tr>
     * <tr><td>{@code http://host/}</td><td>{@code ""}</td></tr>
     * <tr><td>{@code http://username@host/}</td><td>{@code "username"}</td></tr>
     * <tr><td>{@code http://username:password@host/}</td><td>{@code "username"}</td></tr>
     * <tr><td>{@code http://a%20b:c%20d@host/}</td><td>{@code "a b"}</td></tr>
     * </table>
     */
    public String username() {
        return username;
    }

    /**
     * Returns the password, or an empty string if none is set.
     *
     * <p><table summary="">
     * <tr><th>URL</th><th>{@code encodedPassword()}</th></tr>
     * <tr><td>{@code http://host/}</td><td>{@code ""}</td></tr>
     * <tr><td>{@code http://username@host/}</td><td>{@code ""}</td></tr>
     * <tr><td>{@code http://username:password@host/}</td><td>{@code "password"}</td></tr>
     * <tr><td>{@code http://a%20b:c%20d@host/}</td><td>{@code "c%20d"}</td></tr>
     * </table>
     */
    public String encodedPassword() {
        if (password.isEmpty()) {
            return "";
        }
        int passwordStart = url.indexOf(':', scheme.length() + 3) + 1;
        int passwordEnd = url.indexOf('@');
        return url.substring(passwordStart, passwordEnd);
    }

    /**
     * Returns the decoded password, or an empty string if none is present.
     *
     * <p><table summary="">
     * <tr><th>URL</th><th>{@code password()}</th></tr>
     * <tr><td>{@code http://host/}</td><td>{@code ""}</td></tr>
     * <tr><td>{@code http://username@host/}</td><td>{@code ""}</td></tr>
     * <tr><td>{@code http://username:password@host/}</td><td>{@code "password"}</td></tr>
     * <tr><td>{@code http://a%20b:c%20d@host/}</td><td>{@code "c d"}</td></tr>
     * </table>
     */
    public String password() {
        return password;
    }

    /**
     * Returns the host address suitable for use with {@link InetAddress#getAllByName(String)}. May
     * be:
     *
     * <ul>
     *   <li>A regular host name, like {@code android.com}.
     *   <li>An IPv4 address, like {@code 127.0.0.1}.
     *   <li>An IPv6 address, like {@code ::1}. Note that there are no square braces.
     *   <li>An encoded IDN, like {@code xn--n3h.net}.
     * </ul>
     *
     * <p><table summary="">
     *   <tr><th>URL</th><th>{@code host()}</th></tr>
     *   <tr><td>{@code http://android.com/}</td><td>{@code "android.com"}</td></tr>
     *   <tr><td>{@code http://127.0.0.1/}</td><td>{@code "127.0.0.1"}</td></tr>
     *   <tr><td>{@code http://[::1]/}</td><td>{@code "::1"}</td></tr>
     *   <tr><td>{@code http://xn--n3h.net/}</td><td>{@code "xn--n3h.net"}</td></tr>
     * </table>
     */
    public String host() {
        return host;
    }

    /**
     * Returns the explicitly-specified port if one was provided, or the default port for this URL's
     * scheme. For example, this returns 8443 for {@code https://square.com:8443/} and 443 for {@code
     * https://square.com/}. The result is in {@code [1..65535]}.
     *
     * <p><table summary="">
     * <tr><th>URL</th><th>{@code port()}</th></tr>
     * <tr><td>{@code http://host/}</td><td>{@code 80}</td></tr>
     * <tr><td>{@code http://host:8000/}</td><td>{@code 8000}</td></tr>
     * <tr><td>{@code https://host/}</td><td>{@code 443}</td></tr>
     * </table>
     */
    public int port() {
        return port;
    }

    /**
     * Returns the number of segments in this URL's path. This is also the number of slashes in the
     * URL's path, like 3 in {@code http://host/a/b/c}. This is always at least 1.
     *
     * <p><table summary="">
     * <tr><th>URL</th><th>{@code pathSize()}</th></tr>
     * <tr><td>{@code http://host/}</td><td>{@code 1}</td></tr>
     * <tr><td>{@code http://host/a/b/c}</td><td>{@code 3}</td></tr>
     * <tr><td>{@code http://host/a/b/c/}</td><td>{@code 4}</td></tr>
     * </table>
     */
    public int pathSize() {
        return pathSegments.size();
    }

    /**
     * Returns the entire path of this URL encoded for use in HTTP resource resolution. The returned
     * path will start with {@code "/"}.
     *
     * <p><table summary="">
     * <tr><th>URL</th><th>{@code encodedPath()}</th></tr>
     * <tr><td>{@code http://host/}</td><td>{@code "/"}</td></tr>
     * <tr><td>{@code http://host/a/b/c}</td><td>{@code "/a/b/c"}</td></tr>
     * <tr><td>{@code http://host/a/b%20c/d}</td><td>{@code "/a/b%20c/d"}</td></tr>
     * </table>
     */
    public String encodedPath() {
        int pathStart = url.indexOf('/', scheme.length() + 3); // "://".length() == 3.
        int pathEnd = Util.delimiterOffset(url, pathStart, url.length(), "?#");
        return url.substring(pathStart, pathEnd);
    }

    /**
     * Returns a list of encoded path segments like {@code ["a", "b", "c"]} for the URL {@code
     * http://host/a/b/c}. This list is never empty though it may contain a single empty string.
     *
     * <p><table summary="">
     * <tr><th>URL</th><th>{@code encodedPathSegments()}</th></tr>
     * <tr><td>{@code http://host/}</td><td>{@code [""]}</td></tr>
     * <tr><td>{@code http://host/a/b/c}</td><td>{@code ["a", "b", "c"]}</td></tr>
     * <tr><td>{@code http://host/a/b%20c/d}</td><td>{@code ["a", "b%20c", "d"]}</td></tr>
     * </table>
     */
    public List<String> encodedPathSegments() {
        int pathStart = url.indexOf('/', scheme.length() + 3);
        int pathEnd = Util.delimiterOffset(url, pathStart, url.length(), "?#");
        List<String> result = new ArrayList<>();
        for (int i = pathStart; i < pathEnd; ) {
            i++; // Skip the '/'.
            int segmentEnd = Util.delimiterOffset(url, i, pathEnd, '/');
            result.add(url.substring(i, segmentEnd));
            i = segmentEnd;
        }
        return result;
    }

    /**
     * Returns a list of path segments like {@code ["a", "b", "c"]} for the URL {@code
     * http://host/a/b/c}. This list is never empty though it may contain a single empty string.
     *
     * <p><table summary="">
     * <tr><th>URL</th><th>{@code pathSegments()}</th></tr>
     * <tr><td>{@code http://host/}</td><td>{@code [""]}</td></tr>
     * <tr><td>{@code http://host/a/b/c"}</td><td>{@code ["a", "b", "c"]}</td></tr>
     * <tr><td>{@code http://host/a/b%20c/d"}</td><td>{@code ["a", "b c", "d"]}</td></tr>
     * </table>
     */
    public List<String> pathSegments() {
        return pathSegments;
    }

    /**
     * Returns the query of this URL, encoded for use in HTTP resource resolution. The returned string
     * may be null (for URLs with no query), empty (for URLs with an empty query) or non-empty (all
     * other URLs).
     *
     * <p><table summary="">
     * <tr><th>URL</th><th>{@code encodedQuery()}</th></tr>
     * <tr><td>{@code http://host/}</td><td>null</td></tr>
     * <tr><td>{@code http://host/?}</td><td>{@code ""}</td></tr>
     * <tr><td>{@code http://host/?a=apple&k=key+lime}</td><td>{@code
     * "a=apple&k=key+lime"}</td></tr>
     * <tr><td>{@code http://host/?a=apple&a=apricot}</td><td>{@code "a=apple&a=apricot"}</td></tr>
     * <tr><td>{@code http://host/?a=apple&b}</td><td>{@code "a=apple&b"}</td></tr>
     * </table>
     */
    public @Nullable
    String encodedQuery() {
        if (queryNamesAndValues == null) {
            return null; // No query.
        }
        int queryStart = url.indexOf('?') + 1;
        int queryEnd = Util.delimiterOffset(url, queryStart, url.length(), '#');
        return url.substring(queryStart, queryEnd);
    }

    /**
     * Returns this URL's query, like {@code "abc"} for {@code http://host/?abc}. Most callers should
     * prefer {@link #queryParameterName} and {@link #queryParameterValue} because these methods offer
     * direct access to individual query parameters.
     *
     * <p><table summary="">
     * <tr><th>URL</th><th>{@code query()}</th></tr>
     * <tr><td>{@code http://host/}</td><td>null</td></tr>
     * <tr><td>{@code http://host/?}</td><td>{@code ""}</td></tr>
     * <tr><td>{@code http://host/?a=apple&k=key+lime}</td><td>{@code "a=apple&k=key
     * lime"}</td></tr>
     * <tr><td>{@code http://host/?a=apple&a=apricot}</td><td>{@code "a=apple&a=apricot"}</td></tr>
     * <tr><td>{@code http://host/?a=apple&b}</td><td>{@code "a=apple&b"}</td></tr>
     * </table>
     */
    public @Nullable
    String query() {
        if (queryNamesAndValues == null) {
            return null; // No query.
        }
        StringBuilder result = new StringBuilder();
        namesAndValuesToQueryString(result, queryNamesAndValues);
        return result.toString();
    }

    /**
     * Returns the number of query parameters in this URL, like 2 for {@code
     * http://host/?a=apple&b=banana}. If this URL has no query this returns 0. Otherwise it returns
     * one more than the number of {@code "&"} separators in the query.
     *
     * <p><table summary="">
     * <tr><th>URL</th><th>{@code querySize()}</th></tr>
     * <tr><td>{@code http://host/}</td><td>{@code 0}</td></tr>
     * <tr><td>{@code http://host/?}</td><td>{@code 1}</td></tr>
     * <tr><td>{@code http://host/?a=apple&k=key+lime}</td><td>{@code 2}</td></tr>
     * <tr><td>{@code http://host/?a=apple&a=apricot}</td><td>{@code 2}</td></tr>
     * <tr><td>{@code http://host/?a=apple&b}</td><td>{@code 2}</td></tr>
     * </table>
     */
    public int querySize() {
        return queryNamesAndValues != null ? queryNamesAndValues.size() / 2 : 0;
    }

    /**
     * Returns the first query parameter named {@code name} decoded using UTF-8, or null if there is
     * no such query parameter.
     *
     * <p><table summary="">
     * <tr><th>URL</th><th>{@code queryParameter("a")}</th></tr>
     * <tr><td>{@code http://host/}</td><td>null</td></tr>
     * <tr><td>{@code http://host/?}</td><td>null</td></tr>
     * <tr><td>{@code http://host/?a=apple&k=key+lime}</td><td>{@code "apple"}</td></tr>
     * <tr><td>{@code http://host/?a=apple&a=apricot}</td><td>{@code "apple"}</td></tr>
     * <tr><td>{@code http://host/?a=apple&b}</td><td>{@code "apple"}</td></tr>
     * </table>
     */
    public @Nullable
    String queryParameter(String name) {
        if (queryNamesAndValues == null) {
            return null;
        }
        for (int i = 0, size = queryNamesAndValues.size(); i < size; i += 2) {
            if (name.equals(queryNamesAndValues.get(i))) {
                return queryNamesAndValues.get(i + 1);
            }
        }
        return null;
    }

    /**
     * Returns the distinct query parameter names in this URL, like {@code ["a", "b"]} for {@code
     * http://host/?a=apple&b=banana}. If this URL has no query this returns the empty set.
     *
     * <p><table summary="">
     * <tr><th>URL</th><th>{@code queryParameterNames()}</th></tr>
     * <tr><td>{@code http://host/}</td><td>{@code []}</td></tr>
     * <tr><td>{@code http://host/?}</td><td>{@code [""]}</td></tr>
     * <tr><td>{@code http://host/?a=apple&k=key+lime}</td><td>{@code ["a", "k"]}</td></tr>
     * <tr><td>{@code http://host/?a=apple&a=apricot}</td><td>{@code ["a"]}</td></tr>
     * <tr><td>{@code http://host/?a=apple&b}</td><td>{@code ["a", "b"]}</td></tr>
     * </table>
     */
    public Set<String> queryParameterNames() {
        if (queryNamesAndValues == null) {
            return Collections.emptySet();
        }
        Set<String> result = new LinkedHashSet<>();
        for (int i = 0, size = queryNamesAndValues.size(); i < size; i += 2) {
            result.add(queryNamesAndValues.get(i));
        }
        return Collections.unmodifiableSet(result);
    }

    /**
     * Returns all values for the query parameter {@code name} ordered by their appearance in this
     * URL. For example this returns {@code ["banana"]} for {@code queryParameterValue("b")} on {@code
     * http://host/?a=apple&b=banana}.
     *
     * <p><table summary="">
     * <tr><th>URL</th><th>{@code queryParameterValues("a")}</th><th>{@code
     * queryParameterValues("b")}</th></tr>
     * <tr><td>{@code http://host/}</td><td>{@code []}</td><td>{@code []}</td></tr>
     * <tr><td>{@code http://host/?}</td><td>{@code []}</td><td>{@code []}</td></tr>
     * <tr><td>{@code http://host/?a=apple&k=key+lime}</td><td>{@code ["apple"]}</td><td>{@code
     * []}</td></tr>
     * <tr><td>{@code http://host/?a=apple&a=apricot}</td><td>{@code ["apple",
     * "apricot"]}</td><td>{@code []}</td></tr>
     * <tr><td>{@code http://host/?a=apple&b}</td><td>{@code ["apple"]}</td><td>{@code
     * [null]}</td></tr>
     * </table>
     */
    public List<String> queryParameterValues(String name) {
        if (queryNamesAndValues == null) {
            return Collections.emptyList();
        }
        List<String> result = new ArrayList<>();
        for (int i = 0, size = queryNamesAndValues.size(); i < size; i += 2) {
            if (name.equals(queryNamesAndValues.get(i))) {
                result.add(queryNamesAndValues.get(i + 1));
            }
        }
        return Collections.unmodifiableList(result);
    }

    /**
     * Returns the name of the query parameter at {@code index}. For example this returns {@code "a"}
     * for {@code queryParameterName(0)} on {@code http://host/?a=apple&b=banana}. This throws if
     * {@code index} is not less than the {@linkplain #querySize query size}.
     *
     * <p><table summary="">
     * <tr><th>URL</th><th>{@code queryParameterName(0)}</th><th>{@code
     * queryParameterName(1)}</th></tr>
     * <tr><td>{@code http://host/}</td><td>exception</td><td>exception</td></tr>
     * <tr><td>{@code http://host/?}</td><td>{@code ""}</td><td>exception</td></tr>
     * <tr><td>{@code http://host/?a=apple&k=key+lime}</td><td>{@code "a"}</td><td>{@code
     * "k"}</td></tr>
     * <tr><td>{@code http://host/?a=apple&a=apricot}</td><td>{@code "a"}</td><td>{@code
     * "a"}</td></tr>
     * <tr><td>{@code http://host/?a=apple&b}</td><td>{@code "a"}</td><td>{@code "b"}</td></tr>
     * </table>
     */
    public String queryParameterName(int index) {
        if (queryNamesAndValues == null) {
            throw new IndexOutOfBoundsException();
        }
        return queryNamesAndValues.get(index * 2);
    }

    /**
     * Returns the value of the query parameter at {@code index}. For example this returns {@code
     * "apple"} for {@code queryParameterName(0)} on {@code http://host/?a=apple&b=banana}. This
     * throws if {@code index} is not less than the {@linkplain #querySize query size}.
     *
     * <p><table summary="">
     * <tr><th>URL</th><th>{@code queryParameterValue(0)}</th><th>{@code
     * queryParameterValue(1)}</th></tr>
     * <tr><td>{@code http://host/}</td><td>exception</td><td>exception</td></tr>
     * <tr><td>{@code http://host/?}</td><td>null</td><td>exception</td></tr>
     * <tr><td>{@code http://host/?a=apple&k=key+lime}</td><td>{@code "apple"}</td><td>{@code
     * "key lime"}</td></tr>
     * <tr><td>{@code http://host/?a=apple&a=apricot}</td><td>{@code "apple"}</td><td>{@code
     * "apricot"}</td></tr>
     * <tr><td>{@code http://host/?a=apple&b}</td><td>{@code "apple"}</td><td>null</td></tr>
     * </table>
     */
    public String queryParameterValue(int index) {
        if (queryNamesAndValues == null) {
            throw new IndexOutOfBoundsException();
        }
        return queryNamesAndValues.get(index * 2 + 1);
    }

    /**
     * Returns this URL's encoded fragment, like {@code "abc"} for {@code http://host/#abc}. This
     * returns null if the URL has no fragment.
     *
     * <p><table summary="">
     * <tr><th>URL</th><th>{@code encodedFragment()}</th></tr>
     * <tr><td>{@code http://host/}</td><td>null</td></tr>
     * <tr><td>{@code http://host/#}</td><td>{@code ""}</td></tr>
     * <tr><td>{@code http://host/#abc}</td><td>{@code "abc"}</td></tr>
     * <tr><td>{@code http://host/#abc|def}</td><td>{@code "abc|def"}</td></tr>
     * </table>
     */
    public @Nullable
    String encodedFragment() {
        if (fragment == null) {
            return null;
        }
        int fragmentStart = url.indexOf('#') + 1;
        return url.substring(fragmentStart);
    }

    /**
     * Returns this URL's fragment, like {@code "abc"} for {@code http://host/#abc}. This returns null
     * if the URL has no fragment.
     *
     * <p><table summary="">
     * <tr><th>URL</th><th>{@code fragment()}</th></tr>
     * <tr><td>{@code http://host/}</td><td>null</td></tr>
     * <tr><td>{@code http://host/#}</td><td>{@code ""}</td></tr>
     * <tr><td>{@code http://host/#abc}</td><td>{@code "abc"}</td></tr>
     * <tr><td>{@code http://host/#abc|def}</td><td>{@code "abc|def"}</td></tr>
     * </table>
     */
    public @Nullable
    String fragment() {
        return fragment;
    }

    /**
     * Returns a string with containing this URL with its username, password, query, and fragment
     * stripped, and its path replaced with {@code /...}. For example, redacting {@code
     * http://username:password@example.com/path} returns {@code http://example.com/...}.
     */
    public String redact() {
        return newBuilder("/...")
                .username("")
                .password("")
                .build()
                .toString();
    }

    /**
     * Returns the URL that would be retrieved by following {@code link} from this URL, or null if the
     * resulting URL is not well-formed.
     */
    public @Nullable
    HttpUrl resolve(String link) {
        Builder builder = newBuilder(link);
        return builder != null ? builder.build() : null;
    }

    public Builder newBuilder() {
        Builder result = new Builder();
        result.scheme = scheme;
        result.encodedUsername = encodedUsername();
        result.encodedPassword = encodedPassword();
        result.host = host;
        // If we're set to a default port, unset it in case of a scheme change.
        result.port = port != defaultPort(scheme) ? port : -1;
        result.encodedPathSegments.clear();
        result.encodedPathSegments.addAll(encodedPathSegments());
        result.encodedQuery(encodedQuery());
        result.encodedFragment = encodedFragment();
        return result;
    }

    /**
     * Returns a builder for the URL that would be retrieved by following {@code link} from this URL,
     * or null if the resulting URL is not well-formed.
     */
    public @Nullable
    Builder newBuilder(String link) {
        try {
            return new Builder().parse(this, link);
        } catch (IllegalArgumentException ignored) {
            return null;
        }
    }

    @Override
    public boolean equals(@Nullable Object other) {
        return other instanceof HttpUrl && ((HttpUrl) other).url.equals(url);
    }

    @Override
    public int hashCode() {
        return url.hashCode();
    }

    @Override
    public String toString() {
        return url;
    }

    /**
     * Returns the domain name of this URL's {@link #host()} that is one level beneath the public
     * suffix by consulting the <a href="https://publicsuffix.org">public suffix list</a>. Returns
     * null if this URL's {@link #host()} is an IP address or is considered a public suffix by the
     * public suffix list.
     *
     * <p>In general this method <strong>should not</strong> be used to test whether a domain is
     * valid or routable. Instead, DNS is the recommended source for that information.
     *
     * <p><table summary="">
     * <tr><th>URL</th><th>{@code topPrivateDomain()}</th></tr>
     * <tr><td>{@code http://google.com}</td><td>{@code "google.com"}</td></tr>
     * <tr><td>{@code http://adwords.google.co.uk}</td><td>{@code "google.co.uk"}</td></tr>
     * <tr><td>{@code http://square}</td><td>null</td></tr>
     * <tr><td>{@code http://co.uk}</td><td>null</td></tr>
     * <tr><td>{@code http://localhost}</td><td>null</td></tr>
     * <tr><td>{@code http://127.0.0.1}</td><td>null</td></tr>
     * </table>
     */
    public @Nullable
    String topPrivateDomain() {
        if (Util.verifyAsIpAddress(host)) {
            return null;
        }
        return PublicSuffixDatabase.get().getEffectiveTldPlusOne(host);
    }

    private List<String> percentDecode(List<String> list, boolean plusIsSpace) {
        int size = list.size();
        List<String> result = new ArrayList<>(size);
        for (int i = 0; i < size; i++) {
            String s = list.get(i);
            result.add(s != null ? percentDecode(s, plusIsSpace) : null);
        }
        return Collections.unmodifiableList(result);
    }

    public static final class Builder {

        static final String INVALID_HOST = "Invalid URL host";
        final List<String> encodedPathSegments = new ArrayList<>();
        @Nullable
        String scheme;
        String encodedUsername = "";
        String encodedPassword = "";
        @Nullable
        String host;
        int port = -1;
        @Nullable
        List<String> encodedQueryNamesAndValues;
        @Nullable
        String encodedFragment;

        public Builder() {
            encodedPathSegments.add(""); // The default path is '/' which needs a trailing space.
        }

        /**
         * Returns the index of the ':' in {@code input} that is after scheme characters. Returns -1 if
         * {@code input} does not have a scheme that starts at {@code pos}.
         */
        private static int schemeDelimiterOffset(String input, int pos, int limit) {
            if (limit - pos < 2) {
                return -1;
            }

            char c0 = input.charAt(pos);
            if ((c0 < 'a' || c0 > 'z') && (c0 < 'A' || c0 > 'Z')) {
                return -1; // Not a scheme start char.
            }

            for (int i = pos + 1; i < limit; i++) {
                char c = input.charAt(i);

                if ((c >= 'a' && c <= 'z')
                        || (c >= 'A' && c <= 'Z')
                        || (c >= '0' && c <= '9')
                        || c == '+'
                        || c == '-'
                        || c == '.') {
                    continue; // Scheme character. Keep going.
                } else if (c == ':') {
                    return i; // Scheme prefix!
                } else {
                    return -1; // Non-scheme character before the first ':'.
                }
            }

            return -1; // No ':'; doesn't start with a scheme.
        }

        /**
         * Returns the number of '/' and '\' slashes in {@code input}, starting at {@code pos}.
         */
        private static int slashCount(String input, int pos, int limit) {
            int slashCount = 0;
            while (pos < limit) {
                char c = input.charAt(pos);
                if (c == '\\' || c == '/') {
                    slashCount++;
                    pos++;
                } else {
                    break;
                }
            }
            return slashCount;
        }

        /**
         * Finds the first ':' in {@code input}, skipping characters between square braces "[...]".
         */
        private static int portColonOffset(String input, int pos, int limit) {
            for (int i = pos; i < limit; i++) {
                switch (input.charAt(i)) {
                    case '[':
                        while (++i < limit) {
                            if (input.charAt(i) == ']') {
                                break;
                            }
                        }
                        break;
                    case ':':
                        return i;
                }
            }
            return limit; // No colon.
        }

        private static @Nullable
        String canonicalizeHost(String input, int pos, int limit) {
            // Start by percent decoding the host. The WHATWG spec suggests doing this only after we've
            // checked for IPv6 square braces. But Chrome does it first, and that's more lenient.
            String percentDecoded = percentDecode(input, pos, limit, false);
            return Util.canonicalizeHost(percentDecoded);
        }

        private static int parsePort(String input, int pos, int limit) {
            try {
                // Canonicalize the port string to skip '\n' etc.
                String portString = canonicalize(input, pos, limit, "", false, false, false, true, null);
                int i = Integer.parseInt(portString);
                if (i > 0 && i <= 65535) {
                    return i;
                }
                return -1;
            } catch (NumberFormatException e) {
                return -1; // Invalid port.
            }
        }

        public Builder scheme(String scheme) {
            if (scheme == null) {
                throw new NullPointerException("scheme == null");
            } else if (scheme.equalsIgnoreCase("http")) {
                this.scheme = "http";
            } else if (scheme.equalsIgnoreCase("https")) {
                this.scheme = "https";
            } else {
                throw new IllegalArgumentException("unexpected scheme: " + scheme);
            }
            return this;
        }

        public Builder username(String username) {
            if (username == null) {
                throw new NullPointerException("username == null");
            }
            this.encodedUsername = canonicalize(username, USERNAME_ENCODE_SET, false, false, false, true);
            return this;
        }

        public Builder encodedUsername(String encodedUsername) {
            if (encodedUsername == null) {
                throw new NullPointerException("encodedUsername == null");
            }
            this.encodedUsername = canonicalize(
                    encodedUsername, USERNAME_ENCODE_SET, true, false, false, true);
            return this;
        }

        public Builder password(String password) {
            if (password == null) {
                throw new NullPointerException("password == null");
            }
            this.encodedPassword = canonicalize(password, PASSWORD_ENCODE_SET, false, false, false, true);
            return this;
        }

        public Builder encodedPassword(String encodedPassword) {
            if (encodedPassword == null) {
                throw new NullPointerException("encodedPassword == null");
            }
            this.encodedPassword = canonicalize(
                    encodedPassword, PASSWORD_ENCODE_SET, true, false, false, true);
            return this;
        }

        /**
         * @param host either a regular hostname, International Domain Name, IPv4 address, or IPv6
         *             address.
         */
        public Builder host(String host) {
            if (host == null) {
                throw new NullPointerException("host == null");
            }
            String encoded = canonicalizeHost(host, 0, host.length());
            if (encoded == null) {
                throw new IllegalArgumentException("unexpected host: " + host);
            }
            this.host = encoded;
            return this;
        }

        public Builder port(int port) {
            if (port <= 0 || port > 65535) {
                throw new IllegalArgumentException("unexpected port: " + port);
            }
            this.port = port;
            return this;
        }

        int effectivePort() {
            return port != -1 ? port : defaultPort(scheme);
        }

        public Builder addPathSegment(String pathSegment) {
            if (pathSegment == null) {
                throw new NullPointerException("pathSegment == null");
            }
            push(pathSegment, 0, pathSegment.length(), false, false);
            return this;
        }

        /**
         * Adds a set of path segments separated by a slash (either {@code \} or {@code /}). If {@code
         * pathSegments} starts with a slash, the resulting URL will have empty path segment.
         */
        public Builder addPathSegments(String pathSegments) {
            if (pathSegments == null) {
                throw new NullPointerException("pathSegments == null");
            }
            return addPathSegments(pathSegments, false);
        }

        public Builder addEncodedPathSegment(String encodedPathSegment) {
            if (encodedPathSegment == null) {
                throw new NullPointerException("encodedPathSegment == null");
            }
            push(encodedPathSegment, 0, encodedPathSegment.length(), false, true);
            return this;
        }

        /**
         * Adds a set of encoded path segments separated by a slash (either {@code \} or {@code /}). If
         * {@code encodedPathSegments} starts with a slash, the resulting URL will have empty path
         * segment.
         */
        public Builder addEncodedPathSegments(String encodedPathSegments) {
            if (encodedPathSegments == null) {
                throw new NullPointerException("encodedPathSegments == null");
            }
            return addPathSegments(encodedPathSegments, true);
        }

        private Builder addPathSegments(String pathSegments, boolean alreadyEncoded) {
            int offset = 0;
            do {
                int segmentEnd = Util.delimiterOffset(pathSegments, offset, pathSegments.length(), "/\\");
                boolean addTrailingSlash = segmentEnd < pathSegments.length();
                push(pathSegments, offset, segmentEnd, addTrailingSlash, alreadyEncoded);
                offset = segmentEnd + 1;
            } while (offset <= pathSegments.length());
            return this;
        }

        public Builder setPathSegment(int index, String pathSegment) {
            if (pathSegment == null) {
                throw new NullPointerException("pathSegment == null");
            }
            String canonicalPathSegment = canonicalize(pathSegment, 0, pathSegment.length(),
                    PATH_SEGMENT_ENCODE_SET, false, false, false, true, null);
            if (isDot(canonicalPathSegment) || isDotDot(canonicalPathSegment)) {
                throw new IllegalArgumentException("unexpected path segment: " + pathSegment);
            }
            encodedPathSegments.set(index, canonicalPathSegment);
            return this;
        }

        public Builder setEncodedPathSegment(int index, String encodedPathSegment) {
            if (encodedPathSegment == null) {
                throw new NullPointerException("encodedPathSegment == null");
            }
            String canonicalPathSegment = canonicalize(encodedPathSegment, 0, encodedPathSegment.length(),
                    PATH_SEGMENT_ENCODE_SET, true, false, false, true, null);
            encodedPathSegments.set(index, canonicalPathSegment);
            if (isDot(canonicalPathSegment) || isDotDot(canonicalPathSegment)) {
                throw new IllegalArgumentException("unexpected path segment: " + encodedPathSegment);
            }
            return this;
        }

        public Builder removePathSegment(int index) {
            encodedPathSegments.remove(index);
            if (encodedPathSegments.isEmpty()) {
                encodedPathSegments.add(""); // Always leave at least one '/'.
            }
            return this;
        }

        public Builder encodedPath(String encodedPath) {
            if (encodedPath == null) {
                throw new NullPointerException("encodedPath == null");
            }
            if (!encodedPath.startsWith("/")) {
                throw new IllegalArgumentException("unexpected encodedPath: " + encodedPath);
            }
            resolvePath(encodedPath, 0, encodedPath.length());
            return this;
        }

        public Builder query(@Nullable String query) {
            this.encodedQueryNamesAndValues = query != null
                    ? queryStringToNamesAndValues(canonicalize(
                    query, QUERY_ENCODE_SET, false, false, true, true))
                    : null;
            return this;
        }

        public Builder encodedQuery(@Nullable String encodedQuery) {
            this.encodedQueryNamesAndValues = encodedQuery != null
                    ? queryStringToNamesAndValues(
                    canonicalize(encodedQuery, QUERY_ENCODE_SET, true, false, true, true))
                    : null;
            return this;
        }

        /**
         * Encodes the query parameter using UTF-8 and adds it to this URL's query string.
         */
        public Builder addQueryParameter(String name, @Nullable String value) {
            if (name == null) {
                throw new NullPointerException("name == null");
            }
            if (encodedQueryNamesAndValues == null) {
                encodedQueryNamesAndValues = new ArrayList<>();
            }
            encodedQueryNamesAndValues.add(
                    canonicalize(name, QUERY_COMPONENT_ENCODE_SET, false, false, true, true));
            encodedQueryNamesAndValues.add(value != null
                    ? canonicalize(value, QUERY_COMPONENT_ENCODE_SET, false, false, true, true)
                    : null);
            return this;
        }

        /**
         * Adds the pre-encoded query parameter to this URL's query string.
         */
        public Builder addEncodedQueryParameter(String encodedName, @Nullable String encodedValue) {
            if (encodedName == null) {
                throw new NullPointerException("encodedName == null");
            }
            if (encodedQueryNamesAndValues == null) {
                encodedQueryNamesAndValues = new ArrayList<>();
            }
            encodedQueryNamesAndValues.add(
                    canonicalize(encodedName, QUERY_COMPONENT_REENCODE_SET, true, false, true, true));
            encodedQueryNamesAndValues.add(encodedValue != null
                    ? canonicalize(encodedValue, QUERY_COMPONENT_REENCODE_SET, true, false, true, true)
                    : null);
            return this;
        }

        public Builder setQueryParameter(String name, @Nullable String value) {
            removeAllQueryParameters(name);
            addQueryParameter(name, value);
            return this;
        }

        public Builder setEncodedQueryParameter(String encodedName, @Nullable String encodedValue) {
            removeAllEncodedQueryParameters(encodedName);
            addEncodedQueryParameter(encodedName, encodedValue);
            return this;
        }

        public Builder removeAllQueryParameters(String name) {
            if (name == null) {
                throw new NullPointerException("name == null");
            }
            if (encodedQueryNamesAndValues == null) {
                return this;
            }
            String nameToRemove = canonicalize(
                    name, QUERY_COMPONENT_ENCODE_SET, false, false, true, true);
            removeAllCanonicalQueryParameters(nameToRemove);
            return this;
        }

        public Builder removeAllEncodedQueryParameters(String encodedName) {
            if (encodedName == null) {
                throw new NullPointerException("encodedName == null");
            }
            if (encodedQueryNamesAndValues == null) {
                return this;
            }
            removeAllCanonicalQueryParameters(
                    canonicalize(encodedName, QUERY_COMPONENT_REENCODE_SET, true, false, true, true));
            return this;
        }

        private void removeAllCanonicalQueryParameters(String canonicalName) {
            for (int i = encodedQueryNamesAndValues.size() - 2; i >= 0; i -= 2) {
                if (canonicalName.equals(encodedQueryNamesAndValues.get(i))) {
                    encodedQueryNamesAndValues.remove(i + 1);
                    encodedQueryNamesAndValues.remove(i);
                    if (encodedQueryNamesAndValues.isEmpty()) {
                        encodedQueryNamesAndValues = null;
                        return;
                    }
                }
            }
        }

        public Builder fragment(@Nullable String fragment) {
            this.encodedFragment = fragment != null
                    ? canonicalize(fragment, FRAGMENT_ENCODE_SET, false, false, false, false)
                    : null;
            return this;
        }

        public Builder encodedFragment(@Nullable String encodedFragment) {
            this.encodedFragment = encodedFragment != null
                    ? canonicalize(encodedFragment, FRAGMENT_ENCODE_SET, true, false, false, false)
                    : null;
            return this;
        }

        /**
         * Re-encodes the components of this URL so that it satisfies (obsolete) RFC 2396, which is
         * particularly strict for certain components.
         */
        Builder reencodeForUri() {
            for (int i = 0, size = encodedPathSegments.size(); i < size; i++) {
                String pathSegment = encodedPathSegments.get(i);
                encodedPathSegments.set(i,
                        canonicalize(pathSegment, PATH_SEGMENT_ENCODE_SET_URI, true, true, false, true));
            }
            if (encodedQueryNamesAndValues != null) {
                for (int i = 0, size = encodedQueryNamesAndValues.size(); i < size; i++) {
                    String component = encodedQueryNamesAndValues.get(i);
                    if (component != null) {
                        encodedQueryNamesAndValues.set(i,
                                canonicalize(component, QUERY_COMPONENT_ENCODE_SET_URI, true, true, true, true));
                    }
                }
            }
            if (encodedFragment != null) {
                encodedFragment = canonicalize(
                        encodedFragment, FRAGMENT_ENCODE_SET_URI, true, true, false, false);
            }
            return this;
        }

        public HttpUrl build() {
            if (scheme == null) {
                throw new IllegalStateException("scheme == null");
            }
            if (host == null) {
                throw new IllegalStateException("host == null");
            }
            return new HttpUrl(this);
        }

        @Override
        public String toString() {
            StringBuilder result = new StringBuilder();
            if (scheme != null) {
                result.append(scheme);
                result.append("://");
            } else {
                result.append("//");
            }

            if (!encodedUsername.isEmpty() || !encodedPassword.isEmpty()) {
                result.append(encodedUsername);
                if (!encodedPassword.isEmpty()) {
                    result.append(':');
                    result.append(encodedPassword);
                }
                result.append('@');
            }

            if (host != null) {
                if (host.indexOf(':') != -1) {
                    // Host is an IPv6 address.
                    result.append('[');
                    result.append(host);
                    result.append(']');
                } else {
                    result.append(host);
                }
            }

            if (port != -1 || scheme != null) {
                int effectivePort = effectivePort();
                if (scheme == null || effectivePort != defaultPort(scheme)) {
                    result.append(':');
                    result.append(effectivePort);
                }
            }

            pathSegmentsToString(result, encodedPathSegments);

            if (encodedQueryNamesAndValues != null) {
                result.append('?');
                namesAndValuesToQueryString(result, encodedQueryNamesAndValues);
            }

            if (encodedFragment != null) {
                result.append('#');
                result.append(encodedFragment);
            }

            return result.toString();
        }

        Builder parse(@Nullable HttpUrl base, String input) {
            int pos = Util.skipLeadingAsciiWhitespace(input, 0, input.length());
            int limit = Util.skipTrailingAsciiWhitespace(input, pos, input.length());

            // Scheme.
            int schemeDelimiterOffset = schemeDelimiterOffset(input, pos, limit);
            if (schemeDelimiterOffset != -1) {
                if (input.regionMatches(true, pos, "https:", 0, 6)) {
                    this.scheme = "https";
                    pos += "https:".length();
                } else if (input.regionMatches(true, pos, "http:", 0, 5)) {
                    this.scheme = "http";
                    pos += "http:".length();
                } else {
                    throw new IllegalArgumentException("Expected URL scheme 'http' or 'https' but was '"
                            + input.substring(0, schemeDelimiterOffset) + "'");
                }
            } else if (base != null) {
                this.scheme = base.scheme;
            } else {
                throw new IllegalArgumentException(
                        "Expected URL scheme 'http' or 'https' but no colon was found");
            }

            // Authority.
            boolean hasUsername = false;
            boolean hasPassword = false;
            int slashCount = slashCount(input, pos, limit);
            if (slashCount >= 2 || base == null || !base.scheme.equals(this.scheme)) {
                // Read an authority if either:
                //  * The input starts with 2 or more slashes. These follow the scheme if it exists.
                //  * The input scheme exists and is different from the base URL's scheme.
                //
                // The structure of an authority is:
                //   username:password@host:port
                //
                // Username, password and port are optional.
                //   [username[:password]@]host[:port]
                pos += slashCount;
                authority:
                while (true) {
                    int componentDelimiterOffset = Util.delimiterOffset(input, pos, limit, "@/\\?#");
                    int c = componentDelimiterOffset != limit
                            ? input.charAt(componentDelimiterOffset)
                            : -1;
                    switch (c) {
                        case '@':
                            // User info precedes.
                            if (!hasPassword) {
                                int passwordColonOffset = Util.delimiterOffset(
                                        input, pos, componentDelimiterOffset, ':');
                                String canonicalUsername = canonicalize(input, pos, passwordColonOffset,
                                        USERNAME_ENCODE_SET, true, false, false, true, null);
                                this.encodedUsername = hasUsername
                                        ? this.encodedUsername + "%40" + canonicalUsername
                                        : canonicalUsername;
                                if (passwordColonOffset != componentDelimiterOffset) {
                                    hasPassword = true;
                                    this.encodedPassword = canonicalize(input, passwordColonOffset + 1,
                                            componentDelimiterOffset, PASSWORD_ENCODE_SET, true, false, false, true,
                                            null);
                                }
                                hasUsername = true;
                            } else {
                                this.encodedPassword = this.encodedPassword + "%40" + canonicalize(input, pos,
                                        componentDelimiterOffset, PASSWORD_ENCODE_SET, true, false, false, true, null);
                            }
                            pos = componentDelimiterOffset + 1;
                            break;

                        case -1:
                        case '/':
                        case '\\':
                        case '?':
                        case '#':
                            // Host info precedes.
                            int portColonOffset = portColonOffset(input, pos, componentDelimiterOffset);
                            if (portColonOffset + 1 < componentDelimiterOffset) {
                                host = canonicalizeHost(input, pos, portColonOffset);
                                port = parsePort(input, portColonOffset + 1, componentDelimiterOffset);
                                if (port == -1) {
                                    throw new IllegalArgumentException("Invalid URL port: \""
                                            + input.substring(portColonOffset + 1, componentDelimiterOffset) + '"');
                                }
                            } else {
                                host = canonicalizeHost(input, pos, portColonOffset);
                                port = defaultPort(scheme);
                            }
                            if (host == null) {
                                throw new IllegalArgumentException(
                                        INVALID_HOST + ": \"" + input.substring(pos, portColonOffset) + '"');
                            }
                            pos = componentDelimiterOffset;
                            break authority;
                    }
                }
            } else {
                // This is a relative link. Copy over all authority components. Also maybe the path & query.
                this.encodedUsername = base.encodedUsername();
                this.encodedPassword = base.encodedPassword();
                this.host = base.host;
                this.port = base.port;
                this.encodedPathSegments.clear();
                this.encodedPathSegments.addAll(base.encodedPathSegments());
                if (pos == limit || input.charAt(pos) == '#') {
                    encodedQuery(base.encodedQuery());
                }
            }

            // Resolve the relative path.
            int pathDelimiterOffset = Util.delimiterOffset(input, pos, limit, "?#");
            resolvePath(input, pos, pathDelimiterOffset);
            pos = pathDelimiterOffset;

            // Query.
            if (pos < limit && input.charAt(pos) == '?') {
                int queryDelimiterOffset = Util.delimiterOffset(input, pos, limit, '#');
                this.encodedQueryNamesAndValues = queryStringToNamesAndValues(canonicalize(
                        input, pos + 1, queryDelimiterOffset, QUERY_ENCODE_SET, true, false, true, true, null));
                pos = queryDelimiterOffset;
            }

            // Fragment.
            if (pos < limit && input.charAt(pos) == '#') {
                this.encodedFragment = canonicalize(
                        input, pos + 1, limit, FRAGMENT_ENCODE_SET, true, false, false, false, null);
            }

            return this;
        }

        private void resolvePath(String input, int pos, int limit) {
            // Read a delimiter.
            if (pos == limit) {
                // Empty path: keep the base path as-is.
                return;
            }
            char c = input.charAt(pos);
            if (c == '/' || c == '\\') {
                // Absolute path: reset to the default "/".
                encodedPathSegments.clear();
                encodedPathSegments.add("");
                pos++;
            } else {
                // Relative path: clear everything after the last '/'.
                encodedPathSegments.set(encodedPathSegments.size() - 1, "");
            }

            // Read path segments.
            for (int i = pos; i < limit; ) {
                int pathSegmentDelimiterOffset = Util.delimiterOffset(input, i, limit, "/\\");
                boolean segmentHasTrailingSlash = pathSegmentDelimiterOffset < limit;
                push(input, i, pathSegmentDelimiterOffset, segmentHasTrailingSlash, true);
                i = pathSegmentDelimiterOffset;
                if (segmentHasTrailingSlash) {
                    i++;
                }
            }
        }

        /**
         * Adds a path segment. If the input is ".." or equivalent, this pops a path segment.
         */
        private void push(String input, int pos, int limit, boolean addTrailingSlash,
                          boolean alreadyEncoded) {
            String segment = canonicalize(
                    input, pos, limit, PATH_SEGMENT_ENCODE_SET, alreadyEncoded, false, false, true, null);
            if (isDot(segment)) {
                return; // Skip '.' path segments.
            }
            if (isDotDot(segment)) {
                pop();
                return;
            }
            if (encodedPathSegments.get(encodedPathSegments.size() - 1).isEmpty()) {
                encodedPathSegments.set(encodedPathSegments.size() - 1, segment);
            } else {
                encodedPathSegments.add(segment);
            }
            if (addTrailingSlash) {
                encodedPathSegments.add("");
            }
        }

        private boolean isDot(String input) {
            return input.equals(".") || input.equalsIgnoreCase("%2e");
        }

        private boolean isDotDot(String input) {
            return input.equals("..")
                    || input.equalsIgnoreCase("%2e.")
                    || input.equalsIgnoreCase(".%2e")
                    || input.equalsIgnoreCase("%2e%2e");
        }

        /**
         * Removes a path segment. When this method returns the last segment is always "", which means
         * the encoded path will have a trailing '/'.
         *
         * <p>Popping "/a/b/c/" yields "/a/b/". In this case the list of path segments goes from ["a",
         * "b", "c", ""] to ["a", "b", ""].
         *
         * <p>Popping "/a/b/c" also yields "/a/b/". The list of path segments goes from ["a", "b", "c"]
         * to ["a", "b", ""].
         */
        private void pop() {
            String removed = encodedPathSegments.remove(encodedPathSegments.size() - 1);

            // Make sure the path ends with a '/' by either adding an empty string or clearing a segment.
            if (removed.isEmpty() && !encodedPathSegments.isEmpty()) {
                encodedPathSegments.set(encodedPathSegments.size() - 1, "");
            } else {
                encodedPathSegments.add("");
            }
        }
    }
}
